In the last nor'easter, the ocean got on the subway at Aquarium, and it hasn't gotten off. Like a phalanx of manspreaders, it's laid claim to all the seats. Like a voluble crowd after a Red Sox game/July Fourth fireworks/protest, it's filling the aisles--there is no room for anyone else.

By all accounts, it got on without paying. It seeped in through the roof and slid in under the turnstiles. It does not have a monthly pass; it did not stop at the machines to purchase a Charlie card. Like the fabled Charlie himself, will it be forbidden to exit until it pays?

No: MBTA spokespeople tell us that while they take issue with its destructive behavior, the ocean is not being detained on the train.

(Destructive behavior? Seriously? We shake our heads at that remark. There is no sign that the ocean is anything other than a respectful transit passenger. So salt water damages and corrodes--so what? Countless tramping feet and jostling bodies take their toll on trains too. Such things must be categorized as ordinary wear and tear, not willful damage or mischief.)

Yes, the doors have ceased to function, but this should not present a problem for the ocean. It seeped itself in; surely it can reverse the process. And yet, if you go stand on a Blue Line platform and watch the train pass by, there is ocean, cold and abyssal, gazing back at you from every salt-rimed window.

Perhaps it is unsure of its destination. Does it understand it may need to change trains? If it has a hankering to hear a symphony or wants to catch the Escher exhibit, then it should switch to the Green Line. If it is interested in acquiring a credential or in broadening its knowledge--well, there are institutions of higher education crusted like anemones along the entire reef of the MBTA system, though tourists gravitate to the Red Line. But this is nonsense. What is the sum of human wisdom compared to the ocean's own?

We are beginning to suspect that it needs to transfer not to another subway line but to the commuter rail--not the Newburyport/Rockport Line, of course; the ocean is already at Newburyport and Rockport. And not the Plymouth Line--the ocean is already there too. We sense in it an inland urge, and while climate change may one day acquaint it more intimately with Chelsea, Revere, and Lynn, it would take a lot of carbon to bring the sea to Fitchburg or Worcester. And yet all that is dry land today was ocean once--brine thou art and unto brine shalt thou return. The sea seeks reconciliation with its long-estranged children.

That was a great read! Once or twice the Thames has found its way into the Underground, but more often that not it's one of the smaller rivers that run underneath London, like the Fleet, or just a surfeit of run-off rain water.

Isn't there a book called The Rivers of London? (... I know I can search this). I don't know anything about London's rivers, though: I've heard of Fleet Street but didn't realize there was a Fleet River! What a great name.

I think you would enjoy the Rivers of London series. It's by Ben Aaronovitch. One of the themes of the novel is the hidden rivers of London, like the Fleet that were covered over but still run beneath the city. You can't see the Fleet any more, but we went on a guided walk and the guide took us to a drain cover where you could hear the river gurgling away below the road.